There is my best bet what actually happened but they won't admit it.
And the reason the pilot got confused in the transition from the 747 to the 777 is probably something that the alleged American flight instructor who worked at Asiana alluded to - the systematic gaming of the aircraft-specific tests by exchanging test questions on an Asiana bulletin board. They learned the answers mechanically without really internalizing them, much as someone would cram the night before for a test, and then forget everything committed to short-term memory minutes after the test. For tests unrelated to an occupational specialty, that's a little lame, but not such a big deal. Considering that they were being entrusted with a $100m plane and the lives of hundreds of passengers, if this is how the pilot passed the test, he ought to be in prison for negligent homicide.